\name{npsurv}
\alias{npsurv}
\title{Nonparametric Survival Estimates for Censored Data}
\description{
Computes an estimate of a survival curve for censored data
using either the Kaplan-Meier or the Fleming-Harrington method
or computes the predicted survivor function.
For competing risks data it computes the cumulative incidence curve.
This calls the \code{survival} package's \code{survfit.formula}
function.  Attributes of the event time variable are saved (label and
units of measurement).

For competing risks the second argument for \code{Surv} should be the
event state variable, and it should be a factor variable with the first
factor level denoting right-censored observations.
}
\usage{npsurv(formula, data=environment(formula),
              subset, weights, na.action=na.delete, \dots)}
\arguments{
  \item{formula}{
    a formula object, which must have a \code{Surv} object as the
    response on the left of the \code{~} operator and, if desired, terms
    separated by + operators on the right.
    One of the terms may be a \code{strata} object.
    For a single survival curve the right hand side should be \code{~ 1}.
  }
	\item{data,subset,weights,na.action}{see \code{\link[survival]{survfit.formula}}}
  \item{\dots}{see \code{\link[survival]{survfit.formula}}}
}
\value{
an object of class \code{"npsurv"} and \code{"survfit"}.
See \code{survfit.object} for details. Methods defined for \code{survfit}
objects are \code{print}, \code{summary}, \code{plot},\code{lines}, and
\code{points}. 
}
\details{
  see \code{\link[survival]{survfit.formula}} for details
}
\seealso{
\code{\link{survfit.cph}} for survival curves from Cox models.
\code{\link{print}},
\code{\link{plot}},
\code{\link{lines}},
\code{\link[survival]{coxph}},
\code{\link[survival]{strata}},
\code{\link{survplot}}
}
\author{Thomas Lumley \email{tlumley@u.washington.edu} and Terry Therneau}

\examples{
require(survival)
# fit a Kaplan-Meier and plot it
fit <- npsurv(Surv(time, status) ~ x, data = aml)
plot(fit, lty = 2:3)
legend(100, .8, c("Maintained", "Nonmaintained"), lty = 2:3)

# Here is the data set from Turnbull
#  There are no interval censored subjects, only left-censored (status=3),
#  right-censored (status 0) and observed events (status 1)
#
#                             Time
#                         1    2   3   4
# Type of observation
#           death        12    6   2   3
#          losses         3    2   0   3
#      late entry         2    4   2   5
#
tdata <- data.frame(time   = c(1,1,1,2,2,2,3,3,3,4,4,4),
                    status = rep(c(1,0,2),4),
                    n      = c(12,3,2,6,2,4,2,0,2,3,3,5))
fit  <- npsurv(Surv(time, time, status, type='interval') ~ 1,
               data=tdata, weights=n)

#
# Time to progression/death for patients with monoclonal gammopathy
# Competing risk curves (cumulative incidence)
# status variable must be a factor with first level denoting right censoring
m <- upData(mgus1, stop = stop / 365.25, units=c(stop='years'),
            labels=c(stop='Follow-up Time'), subset=start == 0)
f <- npsurv(Surv(stop, event) ~ 1, data=m)

# CI curves are always plotted from 0 upwards, rather than 1 down
plot(f, fun='event', xmax=20, mark.time=FALSE,
     col=2:3, xlab="Years post diagnosis of MGUS")
text(10, .4, "Competing Risk: death", col=3)
text(16, .15,"Competing Risk: progression", col=2)

# Use survplot for enhanced displays of cumulative incidence curves for
# competing risks

survplot(f, state='pcm', n.risk=TRUE, xlim=c(0, 20), ylim=c(0, .5), col=2)
survplot(f, state='death', add=TRUE, col=3)

f <- npsurv(Surv(stop, event) ~ sex, data=m)
survplot(f, state='death', n.risk=TRUE, conf='diffbands')
}
